Medical laboratories, particularly clinical chemistry laboratories, are in need of a compact repeatable dispenser capable of dispensing volumes in the microliter range. The dispenser should be highly accurate, highly precise and essentially maintenance free. The forces which are stimulating this need are both economic and technical: Economic in terms of both the amount of biological sample needed and in terms of the amount of reagents consumed. Technical in terms of the newer procedures such as radio-immune assays which measure concentrations in the nanogram per deciliter range. No dispenser currently available satisfies completely the above requirements. It is the object of the present invention to do so.